1. Field of the Invention
The present invention relates to a method for manufacturing optical fiber preform, and a burner apparatus employed for manufacturing an optical fiber preform that uses this method, in which glass particles are synthesized by reacting a source material gas in oxy-hydrogen flame, and depositing it in the radial direction of the outer periphery of a starting member.
2. Description of the Related Art
Optical fibers are manufactured by drawing an optical fiber preform.
In addition, examples of methods for manufacturing optical fiber preforms include VAD, OVD, MCVD and PCVD methods. In particular, OVD (Outside Vapor Phase Deposition) method is a method for manufacturing optical fiber preforms consisting of synthesizing glass particles by hydrolyzing or oxidizing silicon tetrachloride (SiCl4), germanium tetrachloride (GeCl4) and so forth in flame together with oxygen and hydrogen, depositing the glass particles (soot) in the radial direction of the outer periphery of a conical starting member provided with a glass material that is provided as a core and rotates around its axis to manufacture a porous optical fiber preform by forming a porous layer composed of multiple layers, and converting it to transparent glass while dehydrating and sintering in an electric oven.
The optical fiber manufactured by drawing this optical fiber preform has superior purity and other qualities.
In the OVD method, an end of a burner 10 used in the step in which the porous optical fiber preform is formed has a structure as shown in FIG. 1, for example.
A first nozzle 1 is provided in the center on the end of this burner 10, and a second nozzle 2 is provided on the same central axis as first nozzle 1 around this first nozzle 1. In addition, a third nozzle 3 is similarly provided on the same central axis as first nozzle 1 around the second nozzle 2, and a fourth nozzle 4 is provided on the same central axis as the first nozzle 1 around the third nozzle 3. In addition, a plurality of fifth nozzles 5 having narrow diameter are provided on the concentric circle of the first nozzle 1 between the second nozzle 2 and third nozzle 3.
In addition, the first nozzle 1 serves as a first port 11, the section between the first nozzle 1 and second nozzle 2 serves as a second port 12, the second between the second nozzle 2 and third nozzle 3 serves as a third port 13, the section between the third nozzle 3 and fourth nozzle 4 serves as a fourth port 14, and the fifth nozzle 5 serve as fifth ports 15.
In order to synthesize glass particles in the OVD method, typically, a mixed gas of, for example, SiCl4 and an additive gas such as oxygen or hydrogen, is supplied as a source material gas from the first port 11, a sealing gas comprised of argon and so forth is supplied from the second port 12, hydrogen is supplied from the third port 13, and oxygen is supplied from the fourth port 14 and fifth ports 15.
However, the method for manufacturing optical fiber preform using this burner 10 had the following problems.
When the source material gas, oxygen and hydrogen are supplied into the oxy-hydrogen flame of the burner 10, glass particles are synthesized by a hydrolysis reaction (flame hydrolysis) that occurs in the flame. Although these glass particles are normally deposited on the surface of the starting member, a part of them adhere to the end of the burner 10. In this manner, when the glass particles adhere to the end of the burner 10, the above ports become blocked causing problems such as a defective manufacture of the porous optical fiber preform.
Furthermore, aggregates of the glass particles (SiO2 particles) that have adhered to the end of the burner 10 also adhere to the surface of the porous optical fiber preform after having separated from the burner 10. If the porous optical fiber preform is sintered in this state, bubbles form within the optical fiber preform, thereby preventing the manufacture of a satisfactory optical fiber preform.
In addition, accompanying the increase in demand for high-speed communications in recent years, the manufacture volume of the optical fibers has increased, and the optical fiber preforms are tending to become larger. As a result, the amount of the source material gas used has also increased, thereby resulting in a corresponding increase in the amount of the glass particles adhering to the end of the burner, which in turn has caused the above problems to become more serious.